1. Field of the Invention
The present invention relates to a color selecting electrode mounting frame for a CRT (Cathode Ray Tube) and a process for production of the same.
2. Description of the Related Art
Inside of a CRT, an aperture grille, shadow mask, or other color selecting electrode is placed in front of the fluorescent screen of the panel. The color selecting electrode is attached to a color selecting electrode mounting frame and is positioned with high precision with respect to the electron guns and fluorescent screen.
A color selecting electrode mounting frame according to the prior art is shown in FIG. 1. As shown in FIG. 1, the color selecting electrode mounting frame 2 is comprising a pair of long members 4, 4 and a pair of short members 6, 6 joined to the two end portions of these long members 4, 4.
At the top edge portions of the long members 4, 4 are formed curved surfaces 8, 8 to which two opposing sides of the color selecting electrode 10 are attached. The curved surfaces 8, 8 have curvatures matching with the curvature of the panel glass of the CRT. The color selecting electrode 10 has formed in it apertures 12 for passing the electron beams.
The short members 6, 6 are bent in a substantially U-shape. The short members 6, 6 are bent in a substantially U-shape so as to provide a clearance between the bottom surface of the frame 2 to the color selecting electrode 10.
When producing the color selecting electrode mounting frame 2 of the prior art, the long members 4 and the short members 6 are separately fabricated. When fabricating a long member 4, as shown in FIG. 2A, first an L-sectional shape rod material 14 is produced. This rod material 14 is formed by cold drawing or rolling a circular cross-section rod material.
Next, the rod material 14 is cut into a predetermined length to obtain a long member preform 14a of an L-sectional shape. Next, as shown in FIG. 2B, the long member preform 14a is set between a punch 16 and a die 18 and formed so as to give it a predetermined curvature. Next, as shown in FIG. 2C, the two end portions of the preform 14a are cut off to remove the unnecessary portions 14b of excess lengths of 10 to 15 mm and fabricate the long members 4. At the top edge portion of the long member 4, a curved surface 8 for attachment of one side of the color selecting electrode 10 shown in FIG. 1 is formed.
When producing a short member 6 shown in FIG. 1, first, as shown in FIG. 3A, a square sectional shaped rod material 16 is cut into a predetermined length to obtain a short member preform 16a. This preform 16a, as shown in FIG. 3B, is placed on a roll 22 positioned between a punch 18 and a die 20. The punch 18 is pushed in the direction of the die 20 so as to bend the material into a U-shape.
Next, as shown in FIG. 3C, the two ends of the preform 16a are cut off to remove the unnecessary portions 16b of the excess lengths. Then, as shown in FIG. 3D, the preform 16a is set in an end cutting apparatus 25, where the two end portions of the preform 16a are cut by a cutter 24. Slanted surfaces 26 for joining with the long members 4 are formed at the two end portions of the same, thereby producing the short member 6. During this cutting, the unnecessary portions 16c are cut off and removed. The slanted mating surfaces 26 are formed since the long member 4 is bent to a predetermined curvature and therefore it is necessary to incline the mating surfaces of the short member 6 to enable joining to the end portions of the same.
After the long members 4 and the short members 6 are fabricated in this way, they are joined by welding as shown in FIG. 1.
However, in such a conventional construction of a color selecting electrode mounting frame 2, there are the problems in production mentioned below.
First, when producing a long member 4, production of the rod material 14 shown in FIG. 2A requires a second processing step of drawing an irregular shape or rolling and therefore the unit cost of the materials becomes higher. Further, the length of the preform 14a cut in the step shown in FIG. 2B is made longer than the finished product in consideration of error etc. in the cutting and forming processes. Therefore, there is the problem that, as shown in FIG. 2C, a step of cutting and removing the unnecessary portions 14b after the forming process becomes necessary and there is great waste of materials.
Second, when producing the short members 6, as shown in FIG. 3B, the preform 16a for the short members 6 is bent to a U-shape using the roll 22, so stabilization of the bending process required that a preform longer than the finished product by about 5 percent be prepared. Therefore, as shown in FIG. 3C, after the bending process, a step of cutting and removing the excess unnecessary portions 16b becomes necessary. The unnecessary portions 16b become wasted material.
Third, when producing a short member 6, as shown in FIG. 3D, a cutting apparatus 25 is used to shape the end portions of a preform 16a to form the slanted mating surface 26, so the steps are complicated and precision of the slanted mating surface is difficult to achieve as well and as a result there is the problem of a higher manufacturing cost overall.